
This result can be found from the proof of Theorem 4.3 in [1]}.
 [2]} 
Let \(q \ge s\)  be an integer number.
For any vector \(z \in \mathbb {R}^{n}\)  and any \(s\) -sparse vector \(u \in \mathbb {R}^{n}\) , one has
\(\left\Vert u-\mathcal {H}_{q}(z)\right\Vert _{2} \le \frac{\sqrt{5}+1}{2} \Vert (u-z)_{\Lambda \cup \Omega }\Vert _{2},\) 
